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76                            METALLURGY OP IRON" AND STEEL.
no nitrogen is lost or gained in the interior of the furnace the volume of gas made from 100,000 cubic feet of air will be
-------:--------=132,000 cubic feet.
In other words, the volume of gas will be about one-third more than the volume of air supplied.
SEC. Up.—Rough estimate of the heat value of the gas.—The percentage of nitrogen in the gas runs about 60 per cent., and there are from one to two per cent, of hydrogen and some free oxygen, both the hydrogen and oxygen being often rated as nitrogen by the chemist. The carbonic acid (C02) and the carbonic oxide (CO) sum up about 38 or 39 per cent., and this total is fairly constant even under wide variations in furnace conditions. If, therefore, we have a carbon ratio of 2, the C02 must be about 12.8 per cent, and the 00=25.7 per cent. If the ratio is 3 the C02=9.6 and 00== 28.9. If the ratio is 4 the C02=7.7 and 00=30.8. Any wide deviation from these figures will usually arise from errors in sampling or determinations, or from the presence of unusual amounts of free hydrogen. Abnormal results may be obtained from samples taken over a short period of time, for the gas should be drawn from the furnace in a regular stream during at least one hour, to avoid temporary irregularities. Assuming the value of carbonic oxide to be 3070 cals. per cubic metre=345 B.t.u. per cubic foot, the value of the gas as above given for a carbon ratio of 2 would be 88.7 B.t.n. per cubic foot; with a ratio of 3 it would be 99.7 B.t.u. and with a ratio of 4, 106.3 B.t.u., so that a reduction from .a ratio of 3 to a ratio of 2 means a reduction of 11 per cent, in the calorific value of the gas per unit of volume.
SEC. Ilq.—Steam in gas.—Steam is always present in tunnel head gas, but is generally neglected by the chemist, as special arrangements must be made for its determination. When the ore and coke are dry the gas will carry about 2 per cent, of steam by volume, but when they both carry 10 per cent, by weight of water, as sometimes happens in wet weather, the gas will contain 8 per cent, and the. total volume produced will be 8 per cent, more than shown by the table. Gas with this amount of moisture burns much less readily under the boilers, and there is a loss of energy from